CONFORMATIONAL TRANSITIONS OF FERRICYTOCHROME c IN STRONG INORGANIC ACIDS

摘要

Conformational transitions of horse heart ferricytochrome c (ferricyt c) have been investigated in the presence of strong inorganic acids and their salts by optical absorption spectroscopy,magnetic circular dichroism and circular dichroism.In the presence of acids (HClO_4 or H_2SO_4,pH 2) or their salts (1 M NaClO_4 or Na_2SO_4,pH 2,25 deg C),the three ligation states of ferricyt c heme were identified.One is the high-spin state:Hisl8-Fe-H_2O (40-50%),and two are the low-spin states:His18-Fe-Met80 (30-25%) and Hisl8-Fe-His (30-25%).Under these conditions low temperatures facilitate native heme coordination of ferricyt c.Transition from low-spin to high-spin heme coordination of ferricyt c is complete in 1 M HClO_4 or 3 M H_2SO_4.At the concentration of HClO_4 and H_2SO_4 above 3 M,different behavior in spectral transitions of ferricyt c near the heme is observed.High-spin pentacoordinated ferricyt c with the heme ligand of Hisl8-Fe is formed in 8 M H_2SO_4.This state is unstable at higher concentration of H_2SO_4 and porphyrin ferricyt c is formed.At HClO_4 concentration higher than 3 M,the new,until this time not observed heme coordination structure of ferricyt c originates.